Spotlights on Recent JACS Publications

摘要

Polymer-based materials subjected to stress become susceptible to macroscopic failure-a process driven by fracturing of individual polymer chains. In the search for more stress-responsive materials, chemists have looked to polymer hidden length-a portion of a polymer backbone that is contained within a macrocyclic loop, held together by a chemical bond between non-adjacent backbone atoms. Known as "hidden length" because it does not contribute to the end-to-end distance of the polymer, it can be incorporated in a way that allows release under mechanical loads, providing localized strain relief without chain fracture. To date, hidden length designs have focused mostly on the choice of the sacrificial bond, but Wengui Weng, Wenke Zhang, Roman Boulatov, and co-workers describe a new mechanophore that adds mechanochemical reactivity to the hidden length itself (DOI: 10.1021/jacs.0c09220). The researchers integrate 2,3-diphenyl-cyclobutene-l,4-dicarboxy-late into macrocyclic cinnamate dimers and find that stretching the corresponding polymer more than doubles its length without fracture of the chain. Theoretical calculations, validated with experimental studies, show that breaking the chain by stretching it requires 11 times as much energy as that required for a simple polyester of the same initial length. The study provides evidence of the potential benefits of incorporating mechanochemically active components into polymer hidden length.